In general, in the case of manufacturing a semiconductor device by using a cadmium telluride (CdTe) substrate, CdTe single crystals grown by a vertical gradient freezing method (VGF method) and the like are processed into a flat plate with a desired size, and a surface of the flat plate is polished (subjected to mirror surface polishing), whereby a substrate material for manufacturing the device is prepared. On such a CdTe substrate, a predetermined semiconductor (for example, an HgZnTe film and the like) is epitaxially grown, and a semiconductor device such as an infrared detection element is manufactured.
Heretofore, it has been frequent that a user (substrate user) who has purchased the CdTe substrate performs such epitaxial growth after, as pretreatment, etching the CdTe substrate by approximately from several micrometers (μm) to ten micrometers in order to remove an oxidation film generated in a processing finishing step for a surface of the CdTe substrate and in a subsequent period of storing the substrate.
For example, in Patent Document 1, a general method of such polishing (mirror surface polishing) is disclosed, and in Patent Document 2, a general method of etching treatment is disclosed. Moreover, in Patent Document 3, a process is disclosed, in which a single crystal substrate of Hg0.8Cd0.2Te is polished by a diamond polishing liquid with a particle diameter of 0.5 μm, and is thereafter etched by a 0.5% bromine-methanol solution for two minutes, whereby polishing scratches are removed.